Octahedron rotation evolution in 2D perovskites and its impact on optoelectronic properties: the case of Ba–Zr–S chalcogenides†
Octahedron rotation (OR) is a unique structural feature in most perovskite materials. During dimensional reduction from bulk to two-dimensional (2D) perovskites, how the OR pattern evolves is still an open question. Here, we employ an adapted Glazer's notation from bulk perovskites to systematically study the structural evolution of 2D perovskites by fully considering the possible OR patterns. Applying this approach to the 2D Ba–Zr–S system, we establish the relationship between the OR pattern and slab thickness. It is found that as the thickness decreases, the OR pattern undergoes a transition by suppressing out-of-plane rotations. The OR in 2D chalcogenide perovskites could result in an anti-confinement effect, i.e., reducing the band gap to even below that of the bulk by countering the quantum confinement effect. In addition, we show that the Ba–Zr–S 2D perovskites exhibit reasonable electron mobility of ∼150 cm2 V−1 s−1 and large exciton binding energy of ∼0.9 eV. Combining the slab thickness and strain as effective knobs for widely tuning the electronic structure, we suggest the 2D chalcogenide perovskites as promising optoelectronic materials.